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Equatorial mount Polar alignment without Polaris?

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#1 Maged

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Posted 09 March 2015 - 08:54 AM

Hi,

 

I wanted to ask if it is possible to do polar alignment for my EQ mount without seeing polaris? as Polaris is blocked behind a wall, so is there a way to work around that?

 

Thanks



#2 Brian Carter

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Posted 09 March 2015 - 09:03 AM

You can do drift alignment (google it), but that is a real PITA and not worth it unless you are going to be doing some photography.

 

If you're not interested in photography, you can polar align well enough for good tracking and goto.  Set up the mount and make sure it is level.  Set the elevation angle of the mount for your Latitude and get a compass to point it north.  Then go through your whole alignment stars and you're done.  That should be good enough for tracking and only a few minor corrections here and there.

 

This is actually how I polar align even when I'm at a site where I can see Polaris.  Unless you are doing photography, 'kind-of-close' to polar alignment is totally acceptable. 



#3 Maged

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Posted 09 March 2015 - 09:06 AM

Can you please explain more about whole alignment stars?

 

Thanks



#4 CharlesW

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Posted 09 March 2015 - 09:10 AM

Another choice is TheSkyX from Software Bisque. Its alignment routine allows you to polar align without having Polaris available. It is not inexpensive but it does a lot more than PA.

#5 Brian Carter

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Posted 09 March 2015 - 09:26 AM

Can you please explain more about whole alignment stars?

 

Thanks

 

Sorry, alignment stars are for Goto.  I take it from your question that you don't have goto on your scope.  Alignment stars work with the computer for fancy mounts.  When you get set up and turn it on it asks you to point at relatively bright stars in different parts of the sky, after you do this the mount knows how it is oriented and you can have it automatically find objects for you.

 

But since you don't have that.... You can still do the same procedure I outlined.  Just get a compass and get the mount pointed north to the best of your ability, and adjust the elevation to your latitude.  That is plenty polar aligned for a functional EQ mount.



#6 csrlice12

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Posted 09 March 2015 - 10:27 AM

Brian has the right of it.  I just use a compass as I don't do AP, just visual.....think I paid $4 for the compass at WalMart.....



#7 Abhat

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Posted 09 March 2015 - 10:33 AM

I have used similar method described by Brian when polar aligning my mount during daytime viewing ( Sun, Venus, Jupiter etc). I set the latitude based on my location (40 degrees). Google will tell you the latitude for you zip code. Then using smartphone compass app  I orient the mount in the North direction. Make sure there are no metallic objects near by that could cause magnetic interference.

 

This method is approximate and works well for visual only. It will allow you to track for few minutes without any issues.



#8 Hesiod

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Posted 09 March 2015 - 10:47 AM

You may avoid the compass provided that you know which star is closest to the South at the time you are setting up your telescope (phone "apps", planetary software and the good old paper charts/ephemeris may answer to this question).

 

I do this very often with my non-goto driven Mount and it can be rather effective for visual (especially if the Sun or the shades' angles were employed to guess the S).

 

Just to be clear: the Mount have to be placed facing North, exactly as it were aligned through the polarscope.



#9 dmgriff

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Posted 09 March 2015 - 11:08 AM

Second using the compass, mine has a magnetic declination or magnetic variation offset (google if you are not familiar with the term).

 

I can not see Polaris due to trees, and I do not stoop well to use a polar alignment scope.

 

I have used the compass for eq1, eq3, eq5 gem alignment.

 

You may be surprised at how good a track you can get with a compass polar aligned gem.

 

Good viewing,

 

Dave

 

 

 

 



#10 mrowlands

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Posted 09 March 2015 - 11:17 AM

When using a compass and the latitude scale to set up your mount, it helps if you make sure it is level.  If the mount doesn't have one, you can get an inexpensive bubble level at a hardware store.  Also, since the latitude scales aren't always accurate, it helps if you can align it at least once somewhere that you can see the north star.  Also, make sure the mount is level at that time.  Then you never have to adjust latitude again, providing that you always level it and you don't change your latitude too much!

 

Mike R.



#11 Maged

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Posted 09 March 2015 - 12:21 PM

Thanks all for your really helpful replies.

 

I am actually using the iPhone compass to direct my mount to the north which provides few minutes of visual observation without noticeable drifting.

 

But when I attached my camera to the telescope drifting was so bad. like a 15 seconds exposure of orion nebula will result in a very bad star trails, so I'm trying my best to do accurate aligning.



#12 Brian Carter

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Posted 09 March 2015 - 01:30 PM

Oh, you are doing photography. The compass isn't going to help you, you NEED to be anal about polar alignment. The drift method is your best option, even if you could see Polaris.

#13 mclewis1

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Posted 09 March 2015 - 02:21 PM

I am actually using the iPhone compass to direct my mount to the north which provides few minutes of visual observation without noticeable drifting.

 

But when I attached my camera to the telescope drifting was so bad. like a 15 seconds exposure of orion nebula will result in a very bad star trails, so I'm trying my best to do accurate aligning.

What mount do you have?

What scope (focal length)?

What kind of camera?

 

This will tell us something about your expectations and what you can reasonably expect to be able to do.



#14 Maged

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Posted 09 March 2015 - 02:26 PM

I have an EQ4 mount

 

I have a 4" telescope with 900mm focal length

 

I have a canon 70D camera, Prime focus attached to the telescope

 

 

till not I'm getting very bad quality photos, any exposure more than 4 secs is a disaster 



#15 Starman1

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Posted 09 March 2015 - 06:16 PM

Hi,

 

I wanted to ask if it is possible to do polar alignment for my EQ mount without seeing polaris? as Polaris is blocked behind a wall, so is there a way to work around that?

 

Thanks

Yes.

First, level the tripod before you install the mount, making one leg approximately to the north or south depending where your fine tune azimuth post is located on the mount.

Second, set your mount to read you latitude on the side indicator after installing on the mount.

Third, look up the offset between magnetic north and geographic north for your location.  Magnetic north will be to the west if you are east of Chicago, approximately, and it will be to the east of north if you are west of there.

Fourth, use a compass to identify magnetic north, and turn the compass until the needle points either to the east or west of the N mark by the number of degrees of magnetic offset.  Make sure the mount points at the N marking on the compass, not where the needle points.

Fifth, install the scope and view.  The object will stay in the field more than long enough to watch it visually.

 

For photography, that will not be good enough.  Once you've done the above, you'll have to add

Sixth, Do a drift alignment procedure to dial in the pointing of the mount.  You can easily look up how to do this on-line.  There are many many tutorials.



#16 Kendahl

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Posted 09 March 2015 - 07:28 PM

Do you frequently observe from the same location? If so, get a good polar alignment and mark the locations of your tripod feet. I use magic marker on my concrete driveway and small stakes on grass. The next time you go there, put the tripod feet on the marks. For visual observing, that's good enough. For photography, you will still need to repeat a drift alignment but you will start out close.



#17 SteveNH

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Posted 11 March 2015 - 04:16 PM

Hi Maged, don't let the sound of "drift alignment" scare you away, it is really quite simple if you follow the steps methodically, one step at a time. I do this for short unguided photo sessions and for narrow field planetary photography, and it keeps the target within a few seconds of arc for several minutes, and better if I refine by increasing adjustment iterations. It should vastly decrease your objectionable trailing at a 900mm image scale.

 

First, set up your mount as Don, Brian and others have suggested. This gets you close, as you've seen. 

 

Note that your mount head can be fine-adjusted on its tripod 1) left to right by rotating horizontally, and 2) by changing the inclination of the polar axis with the fine adjustment screw under the south bearing.

 

First, locate Procyon (or other bright star near the equator and close to crossing the meridian, i.e,. in its south-most position) and center it in a medium-high power eyepiece with the drive running. Here is where a 12mm or 9mm crosshair eyepiece comes in handy, but you could still do it without the crosshairs. Note which way you have to nudge the telescope in declination in order to keep the star centered. If it's north, you must rotate the mount head slightly clockwise. If it keeps going towards the south, then turn the mount head slightly counterclockwise (start with about 1 to 2 degrees of adjustment, less as you get closer to not having to nudge at all).

 

Now locate a rising star in the east close to the equator, like Denebola in Leo, and watch its drift as above. If you have to nudge declination to the north, your polar axis is pointing too high and must be lowered. If you nudge to the south, the polar axis is too low, and must be raised. Try changing the tilt about 1 degree at a time to start, and refine as you get closer.

 

Don't be concerned with any drift in right ascension while polar aligning - just compensate for it as needed. Even after you're perfectly polar aligned, it may be necessary to tweak the RA motor speed when tracking.

 

Also, be sure your tube (OTA) with mounted camera is well balanced on the declination axis (by sliding the tube up and down the cradle, as necessary), and that your counterweight balances the total weight of your OTA and camera on the polar axis before doing the drift alignment.



#18 Bart

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Posted 07 July 2016 - 11:36 AM

I was under the impression that if you have a goto system you don't really need the mount to be aligned up with Polaris are even close to it because once you have identified a few alignment stars the computer knows how to compensate for not being anywhere near polar alignment. Yes, no, maybe?

 

Bart



#19 jrcrilly

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Posted 07 July 2016 - 12:46 PM

I was under the impression that if you have a goto system you don't really need the mount to be aligned up with Polaris are even close to it because once you have identified a few alignment stars the computer knows how to compensate for not being anywhere near polar alignment. Yes, no, maybe?

 

Bart

Maybe. It depends on the mount's controller. Meade and Celestron controllers explicitly use stars across the meridian to permit this compensation. So do others. Others do not. Even some higher-end mounts do not, presuming that the user will do a good polar alignment. Takahashi is an example of that.



#20 Phil Sherman

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Posted 08 July 2016 - 09:30 AM

If you have an RA motor on your mount with settable slew rates, you cna use your camera to preform drift alignment in just a few minutes. Photographic drift alignment takes just over one minute per measurement. The procedure is:

 

1. set your slew rate to 1x sidereal

2. set your exposure time to 70 seconds (assumes computer control of the camera)

3. point your scope at the drift measurement location (ie celestial equator near the meridian)

4. Make sure your mount is tracking

5. Start the exposure. Track for 5 seconds, slew E for 30 seconds then slew W for 35 seconds

 

Examine your image. You should see each star as a bright point with a V shaped tail that passes through or by the star. If you're perfectly polar aligned, the V collapses into a line that passes through the center of the star. The width of the V at the star is a measure of drift in pixels over one minute. Adjust the mount in one direction (azimuth) and see if the V gets wider or narrower. If wider, you need to adjust in the other direction. If the V moves to the other side of the star, you moved the mount too far.

 

Once aligned at the first measurement point, point the mount to the second drift alignment point, the celestial equator around 30 degrees above the E or W horizon and repeat the measurement adjusting the altitude of the mount. After doing this alignment point, repeat the process for both alignment points to refine the alignment and check that doing the second point didn't change the first one.

 

Once you're polar aligned, you'll still have periodic error issues. The only cure for these is to get a mount controller that supports a guide camera feeding correction signals to the mount. Your mount should easily allow 30 second exposures with around a 60% success rate without guiding.



#21 Alex McConahay

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Posted 08 July 2016 - 09:49 AM

>>>>>>>if you have a goto system you don't really need the mount to be aligned up with Polaris

 

First off, let's divide this conversation into two parts.

 

If you are going visual, a modern goto system can take care of your needs all night, as long as you do the alignment correctly at the beginning of the evening. You may have to re-synch now and then, but you should be happy for most purposes including finding, visual observing, and sketching.

 

If you are doing photography, you need to be a whole lot more precise. Start, as usual with a compass and level alignment, (and a polar finder scope if you could use one!!). Then do a drift alignment, or one of many others. (But it gets down to drift eventually, even if you are using the method where you record the drift in your camera instead of your eyeball.) I will not repeat the already good advice you have gotten.

 

The reason you need to get an accurate polar alignment for photography is that without it, you will get field rotation. Stars do not move from east to west. In the northern hemisphere, they move from Northeast to South to Northwest. In other words, their path through the heavens is not a straight line seen from a spot on earth, but a big curve. That curve will show in your images, and is called Field Rotation.

 

Goto scopes do not compensate for this field rotation. Their Goto algorithms are for finding stars, not keeping track of camera orientation.

 

By the way, if you are getting visible star trails in less than fifteen seconds, it is not field rotation (or polar alignment at all----assuming you have decent polar alignment). As long as you are compass and level aligned, you should not get star trails in fifteen seconds. (OK, purists, yes, you will get them, but they probably will not be visible.) 

 

Finally--and this applies to visual or photography--you never need it aligned to Polaris.....Polaris is not at the celestial pole, but five eighths or something of a degree off. Minor point. But remember, you align to the celestial pole. It just so happens that right now, Polaris is the nearby marker of that point in the sky.  

 

A Polaris alignment will do for a happy evening of visual, but not for photography.

 

Alex



#22 pedxing

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Posted 11 July 2016 - 07:38 AM

I can't see Polaris from my normal site (blocked by trees) and I do imaging. Here's what I do:

 

1. Level the tripod/mount and use a compass to point it north.

2. Bring up PHD and start taking 0.5 second exposures (you are guiding when you image, aren't you?).

3. Point approximately to the intersection of the celestial equator and the meridian and find a star in PHD.

4. Turn on the "fine grid" overlay.

5. Watch a star's movement in Dec (N-S).

6. Adjust the azimuth and repeat steps 5 and 6 until the star's movement in Dec stops. This normally gets me within 20 arcminutes.

7. Do a calibration in PHD

8. Use PHD's drift alignment tool to fine-tune the alignment. 1-2 arcminutes is close enough if you are guiding and aren't taking super-long exposures.

 

You can do the same thing for the altitude adjustment by pointing west (or east) as low in the sky as you can see. Once I have my altitude adjustment set for my location I don't have to mess with it unless I go to a site that is at a different latitude.

 

This procedure only takes about 10-15 minutes. It helps that I use an off-axis guider (OAG) so that PHD is seeing at my full focal length.


Edited by pedxing, 11 July 2016 - 07:39 AM.


#23 gnowellsct

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Posted 11 July 2016 - 12:38 PM

Hi,

 

I wanted to ask if it is possible to do polar alignment for my EQ mount without seeing polaris? as Polaris is blocked behind a wall, so is there a way to work around that?

 

Thanks

 

For visual observing it can be done with a compass.  You have to find out the magnetic offset for your area, because the magnetic north does not correspond to true north.  A reasonably good $8 or $10 compass will have a line for you to point at true North based on the needle's indication of magnetic north.

 

Stand behind the mount and just mentally extend the north line up the RA axis, move the mount till it is pointed in line with your compass.

 

That takes care of the AZIMUTH or side to side adjustment.

 

The ALTITUDE adjustment is trickier.  For this it is best to take the mount somewhere where you CAN see Polaris and align with a polar scope or by looking through the polar scope tube (if none is provided).  Make sure the mount is very level when you do this--as in, use a level.   When you level your mount at the site where you *can't* see Polaris, you'll automatically get the right approximate altitude.  And that will be your altitude adjustment.

 

Greg N



#24 corax

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Posted 11 July 2016 - 01:37 PM

I find this method to be a good compromise between "level and point north" on the one hand, and full-blown drift alignment on the other:

 

http://www.astro-tom...r_alignment.htm

 

This will get you a few minutes visual observing with little to no Dec tweaking. But for AP, you'll still need drift alignment.



#25 BGeoghegan

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Posted 11 July 2016 - 06:16 PM

One more option for the initial azimuth setup is to use a local reference line and offset from there. If you have parking lot lines, deck boards or other useful lines that can be used for orienting the scope, the rest is easy. Get a satellite view of your site with true North indicated. Calculate the offset to North from the line. Aim the scope accordingly. In my case the parking lot lines are about 41° from North. I put the North tripod foot to the right of the line and the SE foot to the left. Cutting a triangle to use as a template would also work.


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